Abstract: A box assembly has a bottom board respectively connected to a pair of first side boards and a pair of second side boards. The bottom board has a foldable slot at its four edges, and each two facing edges are respectively connected to the pair of first side boards and the pair of second side boards. The pair of first side boards respectively has an assembling end at its two outer sides, and the inner edge of the assembling end has a plurality of engaging protrusions. The pair of second side boards respectively has an engaging end at its two outer sides, the engaging end has an engaging slot, and the inner edge of the engaging end has a plurality of assembling apertures connecting to the engaging slot. The assembling end and the engaging end of the first side boards and the second side boards can be alternated, such that the first side boards respectively has the engaging end, and the second side boards respectively has the assembling end.